@the CRAVER The street kid who had a serious crush on first sight on Amy and took her to that fat pig to protect his little sister. He promised Amy and Shirone he would quit that life after watching their display and thinking on Amy's words that he's just not suited for that kind of life.
@the CRAVER I could be wrong, in precious chapters they called him Jis, but given that he's the only "noteworthy" male side character they met on this island, I think it's him.
Not to forget Falcoa, the fat dude who runs the island through his drugs, was left off the hook by Amy and Co., so it wouldn't be a stretch to say he sought revenge on the kid, beat him to a pulp and did something to his little sister or gang members. And Gis went to the only place he knew he could find actual help.